In a wideband wireless communications system, the signal tends to decrease from the frequency selective fading due to multi-path transmissions. An orthogonal frequency division multiple access (OFDMA) system has thus been proposed to overcome the problem of frequency selective fading by dividing the total bandwidth into a plurality of sub-carriers, such that the bandwidth on each sub-carrier is sufficiently narrow.
The OFDMA systems use an OFDMA modulation technique to multiplex the traffic data of a plurality of mobile stations in both frequency and time. Typically, OFDMA systems are used on both voice and (packet) data communications. Such a wireless network typically involves transmissions of packet data and voice over IP (VoIP) traffic between access networks (AN) and access terminals (AT). The efficient management of voice and data users thus becomes essential to the respective wireless communications network.
Voice traffic, while being a part of a real-time application, is usually discontinuous in nature and comprises large inactive periods. It is often desired to group a number of voice users together and assign them with a set of shared time-frequency resources. The statistical multiplexing gain is achieved among the group members. For example, when the base station has determined a discontinuous transmission (DTX) state for a user in a particular time period, it can assign the user's transmission (e.g., time and/or frequency) resources to another user. The statistical multiplexing gain is also achieved through the early-terminated hybrid automatic request (HARQ) transmissions. For example, once a user acknowledges its VoIP packet, the time and/or frequency resources become available to other group members based on the implemented scheduling algorithm.
In the past, various conventional techniques have been proposed to allow unused transmission resources to be allocated to other users for voice communication. For example, such technique has been proposed in the third generation partnership project 2 (3GPP2).
According to a conventional technique, a unique identifier (e.g., GroupID) is assigned to a group when the group is established. When the AN assigns an AT to the group, the AN associates the AT's unique identifier (e.g., MACIndex) to the GroupID through a group setup message. The message is managed through upper layer signaling carried on a forward link data channel (F-DCH).
The group setup message defines the exact locations of the resource blocks and an order in which the resources are allocated. In the time domain, the set of shared resources is a group of VoIP frames comprising a VoIP interlace pattern. In the frequency domain, the shared resource is typically a set of distributed resource channels (DRCH), although a set of block resource channels (BRCH) could be used also.
Each AT is assigned a unique ordering index within the group, and a fixed interlace offset within a super-frame for its first sub-packet transmission. This is to align the time between successive first transmissions to the vocoder frame duration (e.g., approximately 20 msec).
Once a group of users is established and assigned a set of shared time-frequency resources, a group resource allocation message that uses bitmap signaling is utilized to assign resources to individual users in each VoIP frame. The bitmap signaling is used by base stations to assign resources and by the users to determine their exact resources within the set of shared time-frequency resources. It is used for first sub-packet and subsequent retransmissions.
In conventional OFDMA networks, at any time, most likely, only some of the ATs are active, and hence the group resources assigned to the respective group may not be fully used. Particularly, in a lightly loaded resource group, most of the group resources may be idle. A solution is thus needed to utilize the idled resource groups efficiently.